Information Provided In Connection With Outstanding Debt Of Subsidiaries (Condensed Consolidating Balance Sheet) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012		Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Investments	$ 61,359		$ 60,264
Cash	855		615	[1]	715		614
Insurance and reinsurance balances receivable	4,154		4,147
Reinsurance recoverable on losses and loss expenses	11,530		12,078
Reinsurance recoverable on policy benefits	231		241
Value of business acquired	583		614
Goodwill and other intangible assets	4,909		4,975
Other assets	9,840		9,611
Total assets	93,461		92,545
Unpaid losses and loss expenses	37,082		37,946
Unearned premiums	7,019		6,864
Future policy benefits	4,465		4,470
Short-term debt	1,402		1,401
Long-term debt	4,307		3,360
Trust preferred securities	309		309
Other liabilities	10,935		10,664
Total liabilities	65,519		65,014
Commitments and contingencies
Total shareholders' equity	27,942		27,531		25,431
Total liabilities and shareholders' equity	93,461		92,545
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	28		31
Cash	197		103	[1]	162		106
Investments in subsidiaries	27,836		27,251
Due from subsidiaries and affiliates, net	114		204
Other assets	9		13
Total assets	28,184		27,602
Other liabilities	242		71
Total liabilities	242		71
Total shareholders' equity	27,942		27,531
Total liabilities and shareholders' equity	28,184		27,602
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	32,593		31,074
Cash	560		515	[1]	496		382
Insurance and reinsurance balances receivable	3,658		3,654
Reinsurance recoverable on losses and loss expenses	16,432		17,232
Reinsurance recoverable on policy benefits	1,162		1,187
Value of business acquired	579		610
Goodwill and other intangible assets	4,359		4,419
Other assets	7,830		7,563
Total assets	67,173		66,254
Unpaid losses and loss expenses	30,593		31,356
Unearned premiums	6,000		5,872
Future policy benefits	3,877		3,876
Due to subsidiaries and affiliates, net	358		384
Short-term debt	851		851
Long-term debt	4,307		3,360
Trust preferred securities	309		309
Other liabilities	8,985		8,272
Total liabilities	55,280		54,280
Total shareholders' equity	11,893		11,974
Total liabilities and shareholders' equity	67,173		66,254
Other ACE Limited Subsidiaries And Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	28,738	[2]	29,159	[2]
Cash	98	[2]	(3)	[1],[2]	57	[2]	126	[2]
Insurance and reinsurance balances receivable	496	[2]	493	[2]
Reinsurance recoverable on losses and loss expenses	(4,902)	[2]	(5,154)	[2]
Reinsurance recoverable on policy benefits	(931)	[2]	(946)	[2]
Value of business acquired	4	[2]	4	[2]
Goodwill and other intangible assets	550	[2]	556	[2]
Other assets	2,001	[2]	2,035	[2]
Total assets	26,054	[2]	26,144	[2]
Unpaid losses and loss expenses	6,489	[2]	6,590	[2]
Unearned premiums	1,019	[2]	992	[2]
Future policy benefits	588	[2]	594	[2]
Due to subsidiaries and affiliates, net	(244)	[2]	(180)	[2]
Short-term debt	551	[2]	550	[2]
Other liabilities	1,708	[2]	2,321	[2]
Total liabilities	10,111	[2]	10,867	[2]
Total shareholders' equity	15,943	[2]	15,277	[2]
Total liabilities and shareholders' equity	26,054	[2]	26,144	[2]
Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Investments in subsidiaries	(27,836)	[3]	(27,251)	[3]
Due from subsidiaries and affiliates, net	(114)	[3]	(204)	[3]
Total assets	(27,950)	[3]	(27,455)	[3]
Due to subsidiaries and affiliates, net	(114)	[3]	(204)	[3]
Total liabilities	(114)	[3]	(204)	[3]
Total shareholders' equity	(27,836)	[3]	(27,251)	[3]
Total liabilities and shareholders' equity	$ (27,950)	[3]	$ (27,455)	[3]

[1] ACE maintains two notional multicurrency cash pools (Pools) with a third-party bank. Various ACE entities participate in one or the other of the Pools, pursuant to which credit and debit balances in individual ACE accounts are translated daily into a single currency and pooled on a notional basis. Individual ACE entities are permitted to overdraw on their individual accounts provided the overall Pool balances do not fall below zero. At December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[2] Includes all other subsidiaries of ACE Limited and intercompany eliminations.

[3] Includes ACE Limited parent company eliminations.